Fire on the Mountain: 2 Forests Offer Clues to Yellowstone’s Fate in a Warming World

Second, the fires could burn up larger sections of forest. Small islands of forest often survive even within otherwise burned areas, said Brian Harvey, an ecologist at the University of Washington, and seeds from these preserved areas often blow into the surrounding burned forests or are carried there by animals. This reseeding method is especially important at higher altitudes where lodgepoles don’t produce serotinous cones.

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Credit Photo illustration by Claire O’Neill/The New York Times; photo by Mike Price

“But what we’re seeing now is more homogeneous burning throughout the forests, with fewer islands of unburned areas,” Dr. Harvey said. “When that happens, there are fewer seed sources to replace the stands.”

That’s important here because lodgepoles make up 80 percent of the trees in this heavily forested region, which includes Yellowstone and Grand Teton National Parks, five national forests, and a handful of outlying wildernesses and wildlife refuges. What will happen to these forests if a changing climate means not only old forests burn, but young ones, too?

That’s what Dr. Harvey and his colleague, Monica Turner, an ecologist at the University of Wisconsin, are here investigating. Yellowstone’s recent fires offer a rare natural experiment to see how forests regenerate after burning and reburning at short intervals.

On a blistering summer day in Stumptown, surrounded by blackened dirt and leafless, lifeless trees that offer no relief from the sun, a dozen students and research assistants fanned out on hands and knees. Minutes later, one shouts “Found one!” and the others converge on her discovery: an inch-high baby lodgepole pine peeking up in the shadow of a charred log.

By counting seedlings a year after the most recent fire, the team can calculate how densely new lodgepoles might regrow in Stumptown. Although there could be some late-sprouting seeds and animals might bring in new seeds in the years to come, based on their initial count, the researchers predict there will be around 400 trees per acre here. In Densetown nearby, there are some 32,000 trees per acre.

In addition to becoming sparser, Stumptown’s tree population seems to be diversifying. Aspens came in after the 2000 fire and resprouted after the 2016 fire. Now they are establishing alongside the lodgepoles.

Throughout Yellowstone’s long history of fire and regrowth, forests have tended to come back like Densetown. But climate change may be pushing even these hardy forests past their breaking point, said Dr. Harvey, and how trees regrow in Stumptown could be a sign of things to come. Taken together, their preliminary findings suggest many of Yellowstone’s dense, lodgepole-dominated forests will give way to sparser, more diverse woodlands and meadows.

“When fires burn at short intervals, we have a lot fewer trees coming back,” Dr. Turner said. “It’s still enough for a forest, but it will be sparser than before.”

There are advantages to these sparser forests. More prevalent grasses and aspens provide food for elk and deer, and bird diversity often explodes after a burn. One problem with younger forests burning instead of older ones, Dr. Hutto said, is that some birds are picky when it comes to charred habitats, preferring burned mature forests.

“If your forest doesn’t get very big before it burns, you don’t get the coolest stuff,” he said.

Roy Renkin, a vegetation management specialist at Yellowstone National Park, said that he is skeptical that young forests will burn more frequently, because they do not produce enough fuel.

“It’s an example of linear thinking to say that warmer and drier equals more and bigger fires,” he said. “There are feedbacks and interactions that change the linearity.

Climate change might be altering these fundamental forest dynamics, said William Romme, a forest fire researcher at Colorado State University.

“The big question we’re asking now is, ‘What does the future hold for these forests?’ ” Dr. Romme said. “Are we entering an era in which things aren’t going to behave like they did before?”

Stumptown itself, Dr. Turner noted, is evidence that given the right climate conditions, young forests in Yellowstone can and will reburn. Ultimately, she says, so long as wildfires are not endangering human lives, it is best to let them take their course. Rather than try to preserve forests in their current state, officials should focus on things they can control or mitigate, like pollution, habitat fragmentation and invasive species, she said.

“Change is going to happen,” Dr. Turner said. “But we’ll still have forests. We’ll still have a wide variety of native species. It will still be Yellowstone.”